It is known to use shape memory alloy wire (SMA wire) in association with latch-based mechanisms. Memory alloy wire (or muscle wire) has a unique property in that it will contract (e.g. 4% in length) when it is heated. When used in a latch mechanism, the muscle wire is hooked onto or attached to the latch. When the muscle wire is in its expanded state, the latch can be engaged, and when the muscle wire is in a contracted state, the latch can be disengaged.
U.S. Pat. No. 5,629,662 of Floyd et al. issued May 13, 1997 discloses a low energy memory metal actuated latch (low energy here being in reference to a small amount of energy which needs to be supplied to the memory alloy wire). The patent describes the use of a memory metal actuator including a length of memory wire, in a system for interrupting current flow in a circuit breaker. The actuator is connected to a latch system which enters a release state when the memory wire contracts following receipt of energy. A plunger associated with the latch system is displaceable by stored energy in a spring.
U.S. Pat. No. 6,441,746 of Taborisskiy et al. issued Aug. 27, 2002 teaches an actuating mechanism for a gauge pointer. A muscle wire driven rack gear is operatively connected to a rotatable pointer gear. The rack gear is biased to a gauge at-rest position by a spring member. Upon receiving an electrical signal from a vehicle sensor, the muscle wire contracts, moving the rack member against the spring force to drive the gauge pointer to an appropriate reading on a gauge face. The actuating mechanism of this patent requires current to continually flow through the muscle wire. This consumes more energy than an actuating mechanism which only requires a one time pulse of current through the muscle wire.
U.S. Pat. No. 6,704,615 of Veenstra et al. issued Mar. 9, 2004 describes an object dispenser that includes latchable and unlatchable retainers. The latch mechanism disclosed in this patent includes an SMA wire and a latch pin associated with a spring. In operation, the latch mechanism unlatches a retainer by a latch pin pulling away from a latch edge of the retainer. Retraction of the latch pin is caused by contraction of the SMA wire, which is attached to the latch pin at one end.
Low battery indicators found in low cost consumer electronics are usually in the form of an audio or visible signal such as a speaker or light. The disadvantage of these indicators is that they consume significant amounts of power, continuously from the batteries being checked, just at the time when power needs to be conserved. It is possible to add a low power display such as an LCD panel, but adding one simply to display battery status would add significant complexity and cost to the device.
It is an object of the present invention to provide an improved low battery indicator.